Lithium-ion electrochemical cell, components thereof, and methods of making and using same

ABSTRACT

An electrochemical cell including at least one nitrogen-containing compound is disclosed. The at least one nitrogen-containing compound may form part of or be included in: an anode structure, a cathode structure, an electrolyte and/or a separator of the electrochemical cell. Also disclosed is a battery including the electrochemical cell.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/738,275 filed on Dec. 17, 2012, the disclosure of which isincorporated herein by reference to the extent it does not conflict withthe present disclosure.

FIELD OF INVENTION

The present invention relates generally to lithium-ion electrochemicalcells and lithium-ion electrochemical cell components. Moreparticularly, the invention relates to lithium-ion electrochemical cellsincluding a nitrogen-containing compound, to components thereof, tobatteries including the electrochemical cells, and to methods of formingand using the batteries, electrochemical cells and components.

BACKGROUND OF THE INVENTION

Because of their relatively high energy density and slow loss of chargeover time when not in use, compared to typical rechargeable batteries,lithium-ion batteries have become increasingly popular for use inconsumer electronics and for other applications, including defense,aerospace, and automotive (e.g., electric and hybrid cars). Althoughlithium-ion batteries work relatively well for a variety ofapplications, the batteries can exhibit shortened life and reduced cycleefficiency as the batteries are discharged and recharged, particularlywhen lithium is used as the anode material.

A lithium-ion battery generally includes one or more electrochemicalcells, wherein each electrochemical cell includes an anode, a cathode,an electrolyte, and a separator between the anode and the cathode.During discharge of the battery, lithium ions carry current from ananode to a cathode and through an electrolyte and a separator of theelectrochemical cell. To recharge the battery, an external currentsource of sufficient bias is applied to the battery to cause the lithiumions to flow in a reverse direction—from the cathode to the anode and toredeposit on the anode.

Lithium-ion electrochemical cells may use a variety of materials, suchas carbon, as an anode. However, lithium metal may be particularlyattractive for use as the anode of electrochemical cells because of itsextremely light weight and high energy density, compared, for example,to anodes, such as lithium intercalated carbon anodes, where thepresence of non-electroactive materials increases weight and volume ofthe anode, and thereby reduces the energy density of the cells. Thesefeatures are highly desirable for batteries for portable electronicdevices such as cellular phones and laptop computers, as well aselectric vehicles, military, and aerospace applications, where lowweight is important.

Unfortunately, when lithium metal is used as an anode in lithium-ionbatteries, progressive formation of finely dispersed, high surface arealithium may occur at the anode surface after repeated charging anddischarging of the cell. The high surface area lithium is very reactiveand can react with electrolyte components or become electricallyisolated from the bulk anode material, which in turn can adverselyaffect the cycle efficiency and life of the lithium-ion electrochemicalcell.

Accordingly, improved lithium-ion cells having a lithium anode,components of the cells, batteries including the cells, and method offorming and using the cells are desired.

SUMMARY OF THE INVENTION

The present invention generally relates to lithium-ion electrochemicalcells and batteries, and more particularly, to lithium-ionelectrochemical cells including a lithium anode, a cathode, anelectrolyte, and one or more nitrogen-containing compounds, which may besoluble, relatively or substantially immobile, or substantiallyinsoluble, to components thereof, and to batteries including such cells.It was surprisingly and unexpectedly found that the addition of thenitrogen-containing compounds to lithium-ion electrochemical cellsimproves anode morphology after discharging and charging and increasescycle efficiency and life of the lithium-ion electrochemical cells andbatteries.

In accordance with various embodiments of the invention, a lithium-ionelectrochemical cell includes an anode containing lithium, a cathode(e.g., comprising a metal oxide), a separator, an electrolyte, and oneor more nitrogen-containing compounds—e.g., soluble, substantiallyimmobile and/or substantially insoluble nitrogen-containing compounds,which may initially form part of one or more of the anode, the cathode,the separator, and/or the electrolyte. During operation or cycling ofthe electrochemical cell, the nitrogen-containing compounds may form auniform ion-conductive surface layer on the lithium anode. It is thoughtthat the formation of the ion-conductive surface facilitates uniformdeposition of lithium on the anode during charging of the cell bysuppressing dendrite formation on the anode and growth of highsurface-area lithium.

In accordance with various aspects of the embodiments, thenitrogen-containing compound is selected from the group consisting ofinorganic nitrates, organic nitrates, inorganic nitrites, organicnitrites, nitro compounds, and other N—O and amine compounds, such aspolymers functionalized with amine, nitrate, nitrite, or nitrofunctional groups. In accordance with further aspects of theembodiments, the nitrogen-containing compound(s) are confined orrestricted primarily to a particular area of the cell (e.g., ananode/electrolyte interface). Restricting the mobility of thenitrogen-containing compound(s) may be beneficial, because a desiredresult (e.g., increased cycle efficiency and cycle life) may be achievedwith relatively small quantities of the nitrogen-containing compounds,while mitigating any gas production that may otherwise result.

An electrochemical cell according to exemplary aspects of variousembodiments of the invention includes an electrolyte, an anodecontaining lithium and optionally, binder(s), coating(s) and/orlayer(s), wherein the anode includes one or more nitrogen-containingcompounds as described herein, a cathode including a metal oxide, and aseparator. The anode may include a binder including anitrogen-containing compound and/or a polymer layer including anitrogen-containing compound.

In accordance with yet additional embodiments of the invention, anelectrochemical cell includes an electrolyte (e.g., liquid, solid, orgel) including one or more nitrogen-containing compounds as describedabove, an anode containing lithium, a cathode containing a metal oxide,and a separator.

In accordance with further embodiments of the invention, a cathode foruse with an electrochemical cell includes lithiated metal oxide and anitrogen-containing compound as described herein. The cathode mayinclude a binder including the one or more nitrogen-containingcompounds, or the cathode may include one or more polymer layersincluding the one or more nitrogen-containing compounds.

And, in accordance with yet additional embodiments, a battery includesone or more lithium-ion electrochemical cells, wherein one or more cellsinclude a lithium anode, a metal oxide cathode, an electrolyte, and aseparator, and wherein one or more of the anode, the cathode, theelectrolyte, and the separator include a nitrogen-containing compound.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The exemplary embodiments of the present invention will be described inconnection with the appended drawing figures, in which:

FIG. 1 illustrates an electrochemical cell including anitrogen-containing compound in accordance with exemplary embodiments ofthe invention;

FIG. 2 illustrates an anode in accordance with various exemplaryembodiments of the invention;

FIG. 3 illustrates an anode in accordance with various additionalexemplary embodiments of the invention;

FIG. 4 illustrates discharge capacity as a function of cycle life ofelectrochemical cells;

FIG. 5 illustrates recharge ratio as a function of cycle life ofelectrochemical cells;

FIG. 6 illustrates SEM images of lithium anodes;

FIG. 7 illustrates discharge capacity as a function of cycle for cellsin accordance with exemplary embodiments of the invention;

FIG. 8 illustrates recharge ratio as a function of cycle for cells inaccordance with exemplary embodiments of the invention; and

FIG. 9 illustrates discharge capacity as a function of cycle for cellsin accordance with exemplary embodiments of the invention.

It will be appreciated that the figures are not necessarily drawn toscale. For example, the dimensions of some of the elements in thefigures may be exaggerated relative to other elements to help to improveunderstanding of illustrated embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The description of exemplary embodiments of the present inventionprovided below is merely exemplary and is intended for purposes ofillustration only; the following description is not intended to limitthe scope of the invention disclosed herein.

Various exemplary embodiments of the present invention provide animproved lithium-ion electrochemical cell, and components thereof,suitable for a variety of applications, including, among others,automotive, medical device, portable electronics, aviation, military,and aerospace. Exemplary lithium-ion electrochemical cells, inaccordance with exemplary embodiments, include one or morenitrogen-containing compounds to increase cycle efficiency and increasecycle life, compared to typical lithium-anode, lithium-ion cells. Theincrease cycle efficiency and cycle life is thought to result fromimproved lithium anode morphology, which would otherwise be worse, afterdischarging and charging the electrochemical cell.

FIG. 1 illustrates an electrochemical cell 100, including anitrogen-containing compound, in accordance with various exemplaryembodiments of the invention. Cell 100 includes a cathode 102(optionally including a cathode coating or layer 110), an anode 104, anelectrolyte 106, a separator 108, and optionally includes currentcollectors 112, 114.

Cathode 102 includes an active material. Suitable cathode activematerials for use in cathode 102 and electrochemical cells describedherein include metal oxides, such as LiCoO₂, LiCo_(x)Ni_((1-x))O₂, wherex is between approximately 0.05 and 0.8 (e.g. LiCO_(0.2)Ni_(0.8)O₂),LiCo_(x)Ni_(y)Mn_((1-x-y)) (e.g. LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ orLiNi_(0.4)Co_(0.2)Mn_(0.4)O), LiMn₂O₄, and combinations thereof. As setforth in more detail below, cathode 102 or layer 110 may additionallyinclude one or more nitrogen-containing materials.

“Nitrogen-containing materials,” in accordance with various exemplaryembodiments of the invention, include compounds including an N—O (e.g.,nitro) and/or an amine functional group. In accordance with variousexemplary aspects of these embodiments, the one or morenitrogen-containing compounds include one or more inorganic nitrates,organic nitrates, inorganic nitrites, organic nitrites, nitro compounds,amines, and other compounds including monomers, oligomers and/orpolymers selected from the group consisting of: polyethylene imine,polyphosphazene, polyvinylpyrolidone, polyacrylamide, polyaniline,polyelectrolytes (e.g., having a nitro aliphatic portion as functionalgroup), and amine groups, such as polyacrylamide, polyallylaminde andpolydiallyldimethylammonium chloride, polyimides, polybenzimidazole,polyamides, and the like.

Examples of inorganic nitrates that may be used include, but are notlimited to: lithium nitrate, sodium nitrate, potassium nitrate, calciumnitrate, cesium nitrate, barium nitrate, and ammonium nitrate. Examplesof organic nitrates that may be used include, but are not limited to,pyridine nitrate, guanidine nitrate, and dialkyl imidazolium nitrates.By way of specific examples, a nitrate for use as thenitrogen-containing compound is selected from the group consisting oflithium nitrate, sodium nitrate, potassium nitrate, calcium nitrate,cesium nitrate, barium nitrate, ammonium nitrate, pyridine nitrate, anddialkyl imidazolium nitrates, such as lithium nitrate, pyridine nitrate.

Examples of inorganic nitrites that may be used include, but are notlimited to: lithium nitrite, sodium nitrite, potassium nitrite, calciumnitrite, cesium nitrite, barium nitrite, and ammonium nitrite. Examplesof organic nitrites that may be used include, but are not limited to,ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octylnitrite. By way of specific examples, a nitrite for use as thenitrogen-containing compound is selected from the group consisting oflithium nitrite, sodium nitrite, potassium nitrite, calcium nitrite,cesium nitrite, barium nitrite, ammonium nitrite and ethyl nitrite, suchas lithium nitrite.

Examples of nitro compounds that may be used include, but are notlimited to: nitromethane, nitropropane, nitrobutanes, nitrobenzene,dinitrobenzene, nitrotoluene, dinitrotoluene, nitropyridine,dinitropyridine.

Examples of other organic N—O compounds that may be used include, butare not limited to pyridine n-oxide, alkylpyridine N-oxides, andtetramethyl piperidine N-oxyl (TEMPO).

The polymers and polyelectrolytes for use in accordance with variousexemplary embodiments may be synthesized by, for example, directnitration reactions with nitric acid and monomers, oligomers, and/orpolymers having an aromatic group, such that, for example, nitrofunctional groups are incorporated into the monomers, oligomers, and/orpolymers. Exemplary monomers, oligomers, and/or polymers suitable forthe exemplary polyelectrolytes include polystyrenes, polyarylenes, suchas polysulfones, polyether keytones, ployphenylenes, and the like.

The nitrogen-containing material may be a soluble compound, such as theinorganic nitrates, organic nitrates, inorganic nitrites, organicnitrites, nitro compounds, amines, and other compounds as set forthabove. Or, the nitrogen-containing material may be a substantiallyinsoluble compound in the electrolyte. As used herein, “substantiallyinsoluble” means less than 1% or less than 0.5% solubility of thecompound in the electrolyte; all percents set forth herein are weight ormass percent, unless otherwise noted.

Substantially insoluble compounds can be formed by, for example,attaching an insoluble cation, monomer, oligomer, or polymer, such aspolystyrene or cellulose to a nitrogen-containing compound to formpolynitrostyrene or nitrocellulose. One such substantially insolublecompound is octyl nitrate. Additionally or alternatively, compounds,such as salts of K, Mg, Ca, Sr, Al, aromatic hydrocarbons, or ethers asbutyl ether may be added to the electrolyte to reduce the solubility ofnitrogen-containing compounds, such as inorganic nitrates, organicnitrates, inorganic nitrites, organic nitrites, organic nitro compounds,and the like, such that otherwise soluble or mobile nitrogen-containingmaterials become substantially insoluble and/or substantially immobilein the electrolyte.

Another approach to reducing the mobility and/or solubility ofnitrogen-containing materials, to form substantially insolublenitrogen-containing compounds, includes attaching an N—O (e.g., nitro)and/or amine functional group to a long carbon chain, having, forexample, about 8 to about 25 carbon atoms, to form micellar-typestructures, with the active groups (e.g., nitrates) facing theelectrolyte solution.

Referring again to FIG. 1, in addition to the metal oxide, cathode 102may include binders, electrolytes, and/or conductive additives. Inaccordance with various exemplary embodiments of the invention, themetal oxide, binders, electrolytes, and/or conductive additives arefunctionalized (e.g., with a nitro or amine functional group) and are anitrogen-containing compound.

Cathode 102 may include one or more conductive fillers to provideenhanced electronic conductivity. Conductive fillers can increase theelectrically-conductive properties of a material and may include, forexample, conductive carbons such as carbon black (e.g., Vulcan XC72Rcarbon black, Printex XE2, or Akzo Nobel Ketjen EC-600 JD), graphitefibers, graphite fibrils, graphite powder (e.g., Fluka #50870),activated carbon fibers, carbon fabrics, non-activated carbonnanofibers. Other non-limiting examples of conductive fillers includemetal coated glass particles, metal particles, metal fibers,nanoparticles, nanotubes, nanowires, metal flakes, metal powders, metalfibers, and metal mesh. In some embodiments, a conductive filler mayinclude a conductive polymer. Examples of suitable electroactiveconductive polymers include, but are not limited to, electroactive andelectronically conductive polymers selected from the group consisting ofpolypyrroles, polyanilines, polyphenylenes, polythiophenes, andpolyacetylenes. Other conductive materials known to those of ordinaryskill in the art can also be used as conductive fillers. The amount ofconductive filler, if present, may be present in the range of 2 to 30%by weight of the cathode active layer. In accordance with variousexemplary embodiments of the invention, the filler is functionalizedwith a nitrogen group, such as an N—O or amine group. Cathode 102 mayalso further comprise other additives including, but not limited to,metal oxides, aluminas, silicas, and transition metal chalcogenides,which may additionally or alternatively be functionalized with anitrogen-containing group, such as an amine or N—O group.

If cathode 102 includes a binder, the binder material may be a polymericmaterial. Examples of polymer binder materials include, but are notlimited to, polyvinylidene fluoride (PVDF)-based polymers, such aspoly(vinylidene fluoride) (PVDF), PVF2 and its co- and terpolymers withhexafluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene,poly(vinyl fluoride), polytetrafluoroethylenes (PTFE),ethylene-tetrafluoroethylene copolymers (ETFE), polybutadiene,cyanoethyl cellulose, carboxymethyl cellulose and its blends withstyrene-butadiene rubber, polyacrylonitrile, ethylene-propylene-diene(EPDM) rubbers, ethylene propylene diene terpolymers, styrene-butadienerubbers (SBR), polyimides or ethylene-vinyl acetate copolymers. In somecases, the binder material may be substantially soluble in aqueous fluidcarriers and may include, but is not limited to, cellulose derivatives,typically methylcellulose (MC), carboxy methylcellulose (CMC) andhydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA),polyacrylic acid salts, polyacryl amide (PA), polyvinyl pyrrolidone(PVP) and polyethylene oxides (PEO). In one set of embodiments, thebinder material ispoly(ethylene-co-propylene-co-5-methylene-2-norbornene) (EPMN), whichmay be chemically neutral (e.g., inert) towards cell components. UVcurable acrylates, UV curable methacrylates, and heat curable divinylethers can also be used. The amount of binder, if present, may bepresent in the range of 2 to 30% by weight of the cathode active layer.In accordance with various exemplary embodiments of the invention, thebinder is functionalized with a nitrogen group, such as an N—O (e.g.,nitro) or amine group.

In some embodiments, cathode 102 may also include a conductive poroussupport structure. A porous support structure can comprise any suitableform. In some instances, the porous support structure can comprise aporous agglomeration of discrete particles, within which the particlescan be porous or non-porous. For example, the porous support structuremight be formed by mixing porous or non-porous particles with a binderto form a porous agglomeration. Electrode active material might bepositioned within the interstices between the particles and/or the poreswithin the particles (in cases where porous particles are employed) toform the electrodes described herein.

In some embodiments, the porous support structure can be a “porouscontinuous” structure. A porous continuous structure, as used herein,refers to a continuous solid structure that contains pores within it,with relatively continuous surfaces between regions of the solid thatdefine the pores. Examples of porous continuous structures include, forexample, material that includes pores within its volume (e.g., a porouscarbon particle, a metal foam, etc.). One of ordinary skill in the artwill be capable of differentiating between a porous continuous structureand, for example, a structure that is not a porous continuous structure,but which is a porous agglomeration of discrete articles (where theinterstices and/or other voids between the discrete particles would beconsidered pores) by, for example, comparing SEM images of the twostructures. In accordance with various embodiments of the invention, theporous support includes functional nitrogen groups, such as N—O and/oramine groups and is a nitrogen-containing compound.

The porous support structure may be of any suitable shape or size. Forexample, the support structure can be a porous continuous particle withany suitable maximum cross-sectional dimension (e.g., less than about 10mm, less than about 1 mm, less than about 500 microns, etc.). In somecases, the porous support structure (porous continuous or otherwise) canhave a relatively large maximum cross-sectional dimension (e.g., atleast about 500 microns, at least about 1 mm, at least about 10 mm, atleast about 10 cm, between about 1 mm and about 50 cm, between about 10mm and about 50 cm, or between about 10 mm and about 10 cm). In someembodiments, the maximum cross-sectional dimension of a porous supportstructure within an electrode can be at least about 50%, at least about75%, at least about 90%, at least about 95%, at least about 98%, or atleast about 99% of the maximum cross-sectional dimension of theelectrode formed using the porous continuous structure.

By way of particular examples, cathode 102 may include up to about 20%,or about 0.5% to about 4%, or about 1% to about 2% nitrogen-containingmaterials, for example, materials having functional N—O or amine groups,up to about 40%, or about 2% to about 30%, or about 10 to about 20%filler, and up to about 40%, or about 2% to about 30%, or about 10% toabout 20% binder.

As previously stated, the nitrogen-containing materials may be afunctionalized polymer, metal oxide, filler, and/or binder. Additionallyor alternatively, a nitrogen-containing material may be in the form oflayer 110, formed of, for example, one or more monomers, oligomersand/or polymers selected from one or more of the group consisting of:polyethylene imine, polyphosphazene, polyvinylpyrolidone,polyacrylamide, polyaniline, polyelectrolytes (e.g., having a nitroaliphatic portion as a functional group), and amine groups, such aspolyacrylamide, polyallylaminde and polydiallyldimethylammoniumchloride, polyimides, polybenzimidazole, polyamides, and the like.

Anode 104 may be of any structure suitable for use in a givenelectrochemical cell with a given cathode. Suitable active materials,comprising lithium, for anode 104 include, but are not limited to,lithium metal, such as lithium foil and lithium deposited onto asubstrate, such as a plastic film, and lithium alloys, such aslithium-aluminum alloys and lithium-tin alloys.

In certain embodiments, the thickness of the anode may vary from, e.g.,about greater than 0 to a few microns. For instance, the anode may havea thickness of less than 200 microns, less than 100 microns, less than50 microns, less than 25 microns, less than 10 microns, or less than 5microns and greater than about 0 microns. In accordance with exemplarycells, the bulk of the lithium may be in the cathode, when the cell isinitially assembled. In this case, a cell may be formed without anylithium on the anode; the anode may initially include, for example, aprotective structure comprising one or more polymer layers and one ormore lithium-ion conducting ceramic or glass ceramic layer on a currentcollector, whereby lithium would plate onto the current collectorthrough the protective structure upon charging. Exemplary suitableprotected structures are described in application Ser. No. 13/524,662,entitled Plating Technique for Electrode, filed Jun. 15, 2012, thecontents of which are hereby incorporated herein by reference to theextent the contents do not conflict with the present disclosure. Thechoice of the anode thickness may depend on cell design parameters suchas the excess amount of lithium desired, cycle life, and the thicknessof the cathode electrode. In one embodiment, the thickness of the anodeactive layer is in the range of about 2 to 100 microns (e.g., about 5 to50 microns, about 5 to 25 microns, or about 10 to 25 microns).

Anode 104 may include multiple layers. The layers of the anode may bedeposited by any of a variety of methods generally known in the art,such as physical or chemical vapor deposition methods, extrusion, orelectroplating. Examples of suitable physical or chemical vapordeposition methods include, but are not limited to, thermal evaporation(including, but not limited to, resistive, inductive, radiation, andelectron beam heating), sputtering (including, but not limited to,diode, DC magnetron, RF, RF magnetron, pulsed, dual magnetron, AC, MF,and reactive), chemical vapor deposition, plasma enhanced chemical vapordeposition, laser enhanced chemical vapor deposition, ion plating,cathodic arc, jet vapor deposition, and laser ablation.

Deposition of the layers may be carried out in a vacuum or inertatmosphere to minimize side reactions in the deposited layers whichcould introduce impurities into the layers or which may affect thedesired morphology of the layers. In some embodiments, anode activelayers and the layers of multi-layered structures are deposited in acontinuous fashion in a multistage deposition apparatus.

Alternatively, where the anode comprises a lithium foil, or a lithiumfoil and a substrate, the foil and substrate can be laminated togetherby a lamination process as known in the art.

FIG. 2 illustrates anode 104, including a base electrode material layer202, (e.g., comprising an electroactive material such as lithium) and amulti-layered structure 204, in accordance with various exemplaryembodiments of the invention. In some cases herein, the anode isreferred to as an “anode based material,” “anode active material,” orthe like, and the anode along with any protective structures arereferred to collectively as the “anode.” In the illustrated embodiment,multi-layered structure 204 includes a single-ion conductive material206, a polymeric layer 208 positioned between the base electrodematerial and the single-ion conductive material, and a separation layer210 (e.g., a layer resulting from plasma treatment of the electrode)positioned between the electrode and the polymeric layer. As discussedin more detail below, various components of anode 104 may befunctionalized with a nitrogen group, in accordance with variousexemplary embodiments of the invention.

Multi-layered structure 204 can allow passage of lithium ions and mayimpede the passage of other components that may otherwise damage theanode. Multilayered structure 204 can reduce the number of defects andthereby force at least some of the surface of the base electrodematerial to participate in current conduction, impede high currentdensity-induced surface damage, and/or act as an effective barrier toprotect the anode from certain species (e.g., electrolyte).

In some embodiments, single-ion conductive layer 206 material isnon-polymeric. In certain embodiments, the single-ion conductivematerial layer is defined in part or in whole by a metal layer that ishighly conductive toward lithium and minimally conductive towardelectrons. In other words, the single-ion conductive material may be oneselected to allow lithium ions, but to impede electrons or other ions,from passing across the layer. The metal layer may comprise a metalalloy layer, e.g., a lithiated metal layer. The lithium content of themetal alloy layer may vary from about 0.5% by weight to about 20% byweight, depending, for example, on the specific choice of metal, thedesired lithium ion conductivity, and the desired flexibility of themetal alloy layer. Suitable metals for use in the single-ion conductivematerial include, but are not limited to, Al, Zn, Mg, Ag, Pb, Cd, Bi,Ga, In, Ge, Sb, As, and Sn. Sometimes, a combination of metals, such asthe ones listed above, may be used in a single-ion conductive material.

In other embodiments, single-ion conductive layer 206 material mayinclude a ceramic layer, for example, a single ion conducting glassconductive to lithium ions. Suitable glasses include, but are notlimited to, those that may be characterized as containing a “modifier”portion and a “network” portion, as known in the art. The modifier mayinclude a metal oxide of the metal ion conductive in the glass. Thenetwork portion may include a metal chalcogenide such as, for example, ametal oxide or sulfide. Single-ion conductive layers may include glassylayers comprising a glassy material selected from the group consistingof lithium nitrides, lithium silicates, lithium borates, lithiumaluminates, lithium phosphates, lithium phosphorus oxynitrides, lithiumsilicosulfides, lithium germanosulfides, lithium oxides (e.g., Li2O,LiO, LiO2, LiRO2, where R is a rare earth metal), lithium lanthanumoxides, lithium titanium oxides, lithium borosulfides, lithiumaluminosulfides, and lithium phosphosulfides, and combinations thereof.In one embodiment, the single-ion conductive layer comprises a lithiumphosphorus oxynitride in the form of an electrolyte.

A thickness of single-ion conductive material layer 206 (e.g., within amultilayered structure) may vary over a range from about 1 nm to about10 microns. For instance, the thickness of the single-ion conductivematerial layer may be between 1-10 nm thick, between 10-100 nm thick,between 100-1000 nm thick, between 1-5 microns thick, or between 5-10microns thick. The thickness of a single-ion conductive material layermay be no greater than, e.g., 10 microns thick, no greater than 5microns thick, no greater than 1000 nm thick, no greater than 500 nmthick, no greater than 250 nm thick, no greater than 100 nm thick, nogreater than 50 nm thick, no greater than 25 nm thick, or no greaterthan 10 nm thick. In some cases, the single-ion conductive layer has thesame thickness as a polymer layer in a multi-layered structure.

Single-ion conductive layer 206 may be deposited by any suitable methodsuch as sputtering, electron beam evaporation, vacuum thermalevaporation, laser ablation, chemical vapor deposition (CVD), thermalevaporation, plasma enhanced chemical vacuum deposition (PECVD), laserenhanced chemical vapor deposition, and jet vapor deposition. Thetechnique used may depend on any factor related to the layer beingdeposited, such as the nature of the material being deposited or thethickness of the layer.

In some embodiments, suitable polymer layers for use in a multi-layeredstructure (e.g., such as layer 208) include polymers that are highlyconductive towards lithium and minimally conductive towards electrons.Examples of such polymers include ionically conductive polymers,sulfonated polymers, and hydrocarbon polymers. The selection of thepolymer will be dependent upon a number of factors including theproperties of electrolyte and cathode used in the cell. Suitableionically conductive polymers include, e.g., ionically conductivepolymers known to be useful in solid polymer electrolytes and gelpolymer electrolytes for lithium electrochemical cells, such as, forexample, polyethylene oxides.

Suitable sulfonated polymers may include, e.g., sulfonated siloxanepolymers, sulfonated polystyrene-ethylene-butylene polymers, andsulfonated polystyrene polymers. Suitable hydrocarbon polymers mayinclude, e.g., ethylene-propylene polymers, polystyrene and/or polymers.

Polymer layers 208 of a multi-layered structure 204 can also includecrosslinked polymer materials formed from the polymerization of monomerssuch as alkyl acrylates, glycol acrylates, polyglycol acrylates,polyglycol vinyl ethers, and/or polyglycol divinyl ethers. For example,one such crosslinked polymer material is polydivinyl poly(ethyleneglycol). The crosslinked polymer materials may further comprise salts,for example, lithium salts, to enhance ionic conductivity. In oneembodiment, the polymer layer of the multi-layered structure comprises acrosslinked polymer.

Other classes of polymers that may be suitable for use in a polymerlayer include, but are not limited to, polyamines (e.g., poly(ethyleneimine) and polypropylene imine (PPI)); polyamides (e.g., polyamide(Nylon), poly(ε-caprolactam) (Nylon 6), poly(hexamethylene adipamide)(Nylon 66)), polyimides (e.g., polyimide, polynitrile, andpoly(pyromellitimide-1,4-diphenyl ether) (Kapton)); vinyl polymers(e.g., polyacrylamide, poly(2-vinyl pyridine), poly(N-vinylpyrrolidone),poly(methylcyanoacrylate), poly(ethylcyanoacrylate),poly(butylcyanoacrylate), poly(isobutylcyanoacrylate), poly(vinylacetate), poly (vinyl alcohol), poly(vinyl chloride), poly(vinylfluoride), poly(2-vinyl pyridine), vinyl polymer, polychlorotrifluoroethylene, and poly(isohexylcynaoacrylate)); polyacetals; polyolefins(e.g., poly(butene1), poly(n-pentene-2), polypropylene,polytetrafluoroethylene); polyesters (e.g., polycarbonate, polybutyleneterephthalate, polyhydroxybutyrate); polyethers (poly(ethylene oxide)(PEO), poly(propylene oxide) (PPO), poly(tetramethylene oxide) (PTMO));vinylidene polymers (e.g., polyisobutylene, poly(methyl styrene),poly(methylmethacrylate) (PMMA), poly(vinylidene chloride), andpoly(vinylidene fluoride)); polyaramides (e.g., poly(imino-1,3-phenyleneiminoisophthaloyl) and poly(imino-1,4-phenylene iminoterephthaloyl));polyheteroaromatic compounds (e.g., polybenzimidazole (PBI),polybenzobisoxazole (PBO) and polybenzobisthiazole (PBT));polyheterocyclic compounds (e.g., polypyrrole); polyurethanes; phenolicpolymers (e.g., phenol-formaldehyde); polyalkynes (e.g., polyacetylene);polydienes (e.g., 1,2-polybutadiene, cis or trans-1,4-polybutadiene);polysiloxanes (e.g., poly(dimethylsiloxane) (PDMS),poly(diethylsiloxane) (PDES), polydiphenylsiloxane (PDPS), andpolymethylphenylsiloxane (PMPS)); and inorganic polymers (e.g.,polyphosphazene, polyphosphonate, polysilanes, polysilazanes).

The polymer materials listed above and described herein may furthercomprise salts, for example, lithium salts (e.g., LiSCN, LiBr, LiI,LiClO4, LiAsF6, LiSO3CF3, LiSO3CH3, LiBF4, LiB(Ph)4, LiPF6,LiC(SO2CF3)3, and LiN(SO2CF3)2), to enhance ionic conductivity.

The thickness of polymer layer 208 may vary, e.g., over a range fromabout 0.1 microns to about 100 microns. The thickness of the polymerlayer may depend on, for example, whether it is positioned adjacent theanode or cathode, whether a separator is also present in the cell,and/or the number of polymer layers in the battery. For instance, thethickness of the polymer layer may be between 0.1-1 microns thick,between 1-5 microns thick, between 5-10 microns thick, between 10-30microns thick, or between 30-50 microns thick, between 50-70 micronsthick, or between 50-100 microns thick. In some embodiments, thethickness of a polymer layer may be no greater than, e.g., 50 micronsthick, no greater than 25 microns thick, no greater than 10 micronsthick, no greater than 5 microns thick, no greater than 2.5 micronsthick, no greater than 1 micron thick, no greater than 0.5 micronsthick, or no greater than 0.1 microns thick.

A polymer layer may be deposited by method such as electron beamevaporation, vacuum thermal evaporation, laser ablation, chemical vapordeposition, thermal evaporation, plasma assisted chemical vacuumdeposition, laser enhanced chemical vapor deposition, jet vapordeposition, and extrusion. The polymer layer may also be deposited byspin-coating techniques. The technique used for depositing polymerlayers may depend on any suitable variable, such as the type of materialbeing deposited, or the thickness of the layer. In accordance withvarious embodiments of the invention, the polymer layer isfunctionalized with a nitrogen group as described herein.

As noted in the description with respect to anode 104, illustrated inFIG. 2, in one particular embodiment, protective structure 204,separating base electrode material layer 202 from electrolyte 106,includes polymer layer 208 adjacent either base electrode material layer202 or separation layer 210. In other arrangements, a polymer layer neednot be the first layer adjacent the base electrode material layer orseparation layer. Various arrangements of layers, including variousmulti-layered structures, are described below, in which the first layeradjacent the base electrode material layer may or may not be the polymerlayer. It is to be understood that in all arrangements where anyparticular arrangement of layers is shown, alternate ordering of layersis within the scope of the invention. Notwithstanding these options, oneaspect of the invention includes the particular advantages realized by anon-brittle polymer immediately adjacent either the base electrodematerial layer or separation layer.

A multi-layered structure can include various numbers ofpolymer/single-ion conductive pairs as needed. Generally, amulti-layered structure can have n polymer/single-ion conductive pairs,where n can be determined based on a particular performance criteria fora cell. For example, n can be an integer equal to or greater than 1, orequal to or greater than 2, 3, 4, 5, 6, 7, 10, 15, 20, 40, 60, 100, or1000, etc.

In other embodiments, a multi-layered structure may include a greaternumber of polymer layers than single-ion conductive layers, or a greaternumber of single-ion conductive layers than polymer layers. For example,a multi-layered structure may include n polymer layers and n+1single-ion conductive layers, or n single-ion conductive layers and n+1polymer layers, where n is greater than or equal to 2. For example, nmay equal 2, 3, 4, 5, 6, or 7, or higher. However, as described above,it is immediately adjacent at least one polymer layer and, in at least50%, 70%, 90%, or 95% of the ion-conductive layers, such layers areimmediately adjacent a polymer layer on either side.

Another embodiment includes an embedded layer (e.g., of a protectivelayer such as a single-ion conductive material layer) positioned betweentwo layers of base electrode materials. This is referred to as a“lamanode” structure. FIG. 3 illustrates an exemplary anode 104including a first layer of a base electrode material layer 202 (e.g.,lithium, also referred to as a Li reservoir), embedded layer 302, and asecond layer 304 comprising the base electrode material (a working Lilayer). As illustrated in FIG. 3, second layer 304 is positioned betweenbase electrode material layer 202 and electrolyte 106. Second layer 304may be either in direct contact with the electrolyte, or in indirectcontact with the electrolyte through some form of a surface layer (e.g.,an electrode stabilization or multi-layered structure such as onedescribed herein). The function of the bi-layer anode structure, witheach base electrode material layer separated by an embedded layer 302,will become clearer from the description below. It is noted thatalthough layer 302 is illustrated and described as “embedded” in thisdescription, it is noted that the layer need not be partially or fullyembedded. In many or most cases, layer 302 is a substantially thin,two-sided structure coated on each side by base electrode material, butnot covered by base electrode material at its edges.

In general, in operation of the arrangement shown in FIG. 3, some or allof second layer 304 of the anode is “lost” from the anode upon discharge(when it is converted to lithium ion which moves into the electrolyte).Upon charge, when lithium ion is plated as lithium metal onto the anode,it is plated as portion 304 (or at least some portion of second layer304) above layer 302. Those of ordinary skill in the art are aware thatin electrochemical cells such as those described herein, there is asmall amount of overall lithium loss on each charge/discharge cycle ofthe cell. In the arrangement illustrated in FIG. 3, the thickness oflayer 304 (or the mass of layer 304) can be selected such that most orall of layer 304 is lost upon full discharge of the cell (full“satisfaction” of the cathode; the point at which the cathode can nolonger participate in a charging process due to limitations that wouldbe understood by those of ordinary skill in the art).

In certain embodiments, layer 302 is selected to be one that isconductive to lithium ions. The embedded layer can shield the bottom Lilayer from damage as the high Li+ flux of the first cycle damages thetop Li layer surface. Accordingly, once all of layer 304 is consumed ina particular discharge cycle, further discharge results in oxidation oflithium from layer 202, passage of lithium ion through layer 302, andrelease of lithium ion into the electrolyte. Of course, layer 304 neednot be of a particular mass such that all or nearly all of it isconsumed on first discharge. It may take several discharge/chargecycles, and inherent small amounts of lithium loss through each cycle,to result in the need to draw lithium from section 202 through layer 302and into the electrolyte.

In some embodiments, embedded layer 302 may have a thickness between0.01-1 microns, and may depend on, e.g., the type of material used toform the embedded layer and/or the method of depositing the material.For example, the thickness of the embedded layer may be between 0.01-0.1microns, between 0.1-0.5 microns, or between 0.5-1 microns. In otherembodiments, thicker embedded layers are included. For example, theembedded layer can have a thickness between 1-10 microns, between 10-50microns, or between 50-100 microns.

In some cases, the embedded material can be formed of a polymer, e.g.,including ones listed above that are lithium ion conductive. The polymerfilm can be deposited using techniques such as vacuum based PML, VMT orPECVD techniques. In other cases, an embedded layer can comprise a metalor semiconductor material. Metals and semi-conductors can be depositedby, for example, sputtering.

By way of particular examples, anode 104 includes lithium and at leastone layer of a nitrogen-containing material. The nitrogen-containingmaterial may be a functionalized surface having, for example, and amineor nitro group or include one or more monomers, oligomers and/orpolymers selected from the group consisting of: polyethylene imine,polyphosphazene, polyvinylpyrolidone, polyacrylamide, polyaniline,polyelectrolytes (e.g., having a nitro aliphatic portion as a functionalgroup), and amine groups, such as polyacrylamide, polyallylaminde andpolydiallyldimethylammonium chloride, polyimides, polybenzimidazole,polyamides, and the like. A percent of nitrogen-containing compound aspart of the anode may range from up to about 20%, about 0.5% to about5%, or about 1 to about 2%.

Electrolyte 106 can function as a medium for the storage and transportof ions, and in the special case of solid electrolytes and gelelectrolytes, these materials may additionally function as a separator(e.g., separator 108) between anode 104 and cathode 102. Any suitableliquid, solid, or gel material capable of storing and transporting ionsbetween the anode and the cathode may be used. Electrolyte 106 may beelectronically non-conductive to prevent short circuiting between anode104 and cathode 102.

The electrolyte can comprise one or more ionic electrolyte salts toprovide ionic conductivity and one or more liquid electrolyte solvents,gel polymer materials, or polymer materials.

Suitable non-aqueous electrolytes may include organic electrolytescomprising one or more materials selected from the group consisting ofliquid electrolytes, gel polymer electrolytes, and solid polymerelectrolytes.

Examples of useful non-aqueous liquid electrolyte solvents include, butare not limited to, non-aqueous organic solvents, such as, ethylenecarbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate,propylene carbonate, fluoroethylene carbonate, 1,3-dioxolane,dimetthoxyethane, diethyleneglycol dimethyether, triethyleneglycoldimethyl ether, sulfolane and combinations thereof.

Specific mixtures of solvents include, but are not limited to,1,3-dioxolane and dimethoxyethane, 1,3-dioxolane and diethyleneglycoldimethyl ether, 1,3-dioxolane and triethyleneglycol dimethyl ether, and1,3-dioxolane and sulfolane. The weight ratio of the two solvents in themixtures may vary from about 5 to 95 to 95 to 5. In some embodiments, asolvent mixture comprises dioxolanes (e.g., greater than 40% by weightof dioxolanes).

Liquid electrolyte solvents can also be useful as plasticizers for gelpolymer electrolytes. Examples of useful gel polymer electrolytesinclude, but are not limited to, those comprising one or more polymersselected from the group consisting of polyethylene oxides, polypropyleneoxides, polyacrylonitriles, polysiloxanes, polyimides, polyphosphazenes,polyethers, sulfonated polyimides, perfluorinated membranes (NAFIONresins), polydivinyl polyethylene glycols, polyethylene glycoldiacrylates, polyethylene glycol dimethacrylates, derivatives of theforegoing, copolymers of the foregoing, crosslinked and networkstructures of the foregoing, and blends of the foregoing, andoptionally, one or more plasticizers.

Examples of useful solid polymer electrolytes include, but are notlimited to, those comprising one or more polymers selected from thegroup consisting of polyethylene glycol mono, di or tri acrylatepolymers, poly(ethylene oxide) (PEO), poly(acrylo-nitrile)(PAN),poly(methyl methacrylate) (PMMA) and poly(vinylidine fluoride) (PVDF),derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In addition to electrolyte solvents, gelling agents, and polymers asknown in the art for forming electrolytes, the electrolyte may furthercomprise one or more ionic electrolyte salts, also as known in the art,to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the electrolytesdescribed herein include, but are not limited to, LiPF₆, LiBF₄, lithiumbis(oxalate)borate, LiN(CF₃SO₂)₂, LiN (C₂F₅SO₂)₂, LiAsF₆, LiClO₄, andLiC(CF₃SO₂)₃. The addition of ionic lithium salts to the solvent isoptional. Furthermore, if an ionic N—O additive such as an inorganicnitrate, organic nitrate, inorganic nitrite, or polyelectrolyte is used,it may provide ionic conductivity to the electrolyte in which case noadditional ionic lithium electrolyte salts may be needed.

Additives that may reduce or prevent formation of impurities and/ordepletion of electrochemically active materials, including electrodesand electrolyte materials, during charge/discharge of theelectrochemical cell, may be incorporated into electrochemical cellsdescribed herein.

In some cases, an additive such as an organometallic compound may beincorporated into the electrolyte and may reduce or prevent interactionbetween at least two components or species of the cell to increase theefficiency and/or lifetime of the cell. Typically, electrochemical cellsundergo a charge/discharge cycle involving deposition of metal (e.g.,lithium metal) on the surface of the anode (e.g., a base electrodematerial) upon charging and reaction of the metal on the anode surfaceto form metal ions, upon discharging. The metal ions may diffuse fromthe anode surface into an electrolyte material connecting the cathodewith the anode. The efficiency and uniformity of such processes mayaffect cell performance. For example, lithium metal may interact withone or more species of the electrolyte to substantially irreversiblyform lithium-containing impurities, resulting in undesired depletion ofone or more active components of the cell (e.g., lithium, electrolytesolvents). The incorporation of certain additives within the electrolyteof the cell have been found, in accordance with certain embodimentsdescribed herein, to reduce such interactions and to improve the cyclinglifetime and/or performance of the cell.

In some embodiments, the additive may be any suitable species, or saltthereof, capable of reducing or preventing the depletion of activematerials (e.g., electrodes, electrolyte) within a cell, for example, byreducing formation of lithium-containing impurities within the cell,which may be formed via reaction between lithium and an electrolytematerial. In some embodiments, the additive may be an organic ororganometallic compound, a polymer, salts thereof, or combinationsthereof. In some embodiments, the additive may be a neutral species. Insome embodiments, the additive may be a charged species. Additivesdescribed herein may also be soluble with respect to one or morecomponents of the cell (e.g., the electrolyte). In some cases, theadditive may be an electrochemically active species. For example, theadditive may be a lithium salt which may reduce or prevent depletion oflithium and/or the electrolyte, and may also serve as anelectrochemically active lithium salt.

The additive may be present within (e.g., added to) the electrochemicalcell in an amount sufficient to inhibit (e.g., reduce or prevent)formation of impurities and/or depletion of the active materials withinthe cell. “An amount sufficient to inhibit formation of impuritiesand/or depletion of the active materials within the cell,” in thiscontext, means that the additive is present in a large enough amount toaffect (e.g., reduce) formation of impurities and/or the depletion ofthe active materials, relative to an essentially identical cell lackingthe additive. For example, trace amounts of an additive may not besufficient to inhibit depletion of active materials in the cell. Thoseof ordinary skill in the art may determine whether an additive ispresent in an amount sufficient to affect depletion of active materialswithin an electrochemical device. For example, the additive may beincorporated within a component of an electrochemical cell, such as theelectrolyte, and the electrochemical cell may be monitored over a numberof charge/discharge cycles to observe any changes in the amount,thickness, or morphology of the electrodes or electrolyte, or anychanges in cell performance.

Determination of the amount of change in the active materials over anumber of charge/discharge cycles may determine whether or not theadditive is present in an amount sufficient to inhibit formation ofimpurities and/or depletion of the active materials. In some cases, theadditive may be added to the electrochemical cell in an amountsufficient to inhibit formation of impurities and/or depletion of activematerials in the cell by at least 50%, 60%, 70%, 80%, 90%, or, in somecases, by 100%, as compared to an essentially identical cell over anessentially identical set of charge/discharge cycles, absent theadditive.

In some cases, the additive may have the same chemical structure as aproduct of a reaction between lithium of the anode and a solvent withinthe electrolyte, such as an ester, ether, acetal, ketal, or the like.Examples of such solvents include, but are not limited to,1,2-dimethoxyethane, 1,2-dioxolane, ethylene carbonate, and dimethylcarbonate.

In some cases, the additives described herein may be associated with apolymer. For example, the additives may be combined with a polymermolecule or may be bonded to a polymer molecule. In some cases, theadditive may be a polymer. For example, the additive may have theformula, R′—(O—Li)n, wherein R′ is alkyl or alkoxyalkyl. In someembodiments, an additive is added to an electrochemical cell, whereinthe additive is an electrochemically active species. For example, theadditive can serve as electrolyte salt and can facilitate one or moreprocesses during charge and/or discharge of the cell. In some cases, theadditive may be substantially soluble or miscible with one or morecomponents of the cell. In some cases, the additive may be a salt whichis substantially soluble with respect to the electrolyte. The additivemay serve to reduce or prevent formation of impurities within the celland/or depletion of the active materials, as well as facilitate thecharge-discharge processes within the cell.

Incorporation of additives described herein may allow for the use ofsmaller amounts of lithium and/or electrolyte within an electrochemicalcell, relative to the amounts used in essentially identical cellslacking the additive. As described above, cells lacking the additivesdescribed herein may generate lithium-containing impurities and undergodepletion of active materials (e.g., lithium, electrolyte) duringcharge-discharge cycles of the cell. In some cases, the reaction whichgenerates the lithium-containing impurity may, after a number ofcharge-discharge cycles, stabilize and/or begin to self-inhibit suchthat substantially no additional active material becomes depleted andthe cell may function with the remaining active materials. For cellslacking additives as described herein, this “stabilization” is oftenreached only after a substantial amount of active material has beenconsumed and cell performance has deteriorated. Therefore, in somecases, a relatively large amount of lithium and/or electrolyte has oftenbeen incorporated within cells to accommodate for loss of materialduring consumption of active materials, in order to preserve cellperformance.

Accordingly, incorporation of additives as described herein may reduceand/or prevent depletion of active materials such that the inclusion oflarge amounts of lithium and/or electrolyte within the electrochemicalcell may not be necessary. For example, the additive may be incorporatedinto a cell prior to use of the cell, or in an early stage in thelifetime of the cell (e.g., less than five charge-discharge cycles),such that little or substantially no depletion of active material mayoccur upon charging or discharging of the cell. By reducing and/oreliminating the need to accommodate for active material loss duringcharge-discharge of the cell, relatively small amounts of lithium may beused to fabricate cells and devices as described herein. In someembodiments, devices described herein comprise an electrochemical cellhaving been charged and discharged less than five times in its lifetime,wherein the cell comprises an anode comprising lithium, a cathode, andan electrolyte, wherein the anode comprises no more than five times theamount of lithium which can be ionized during one full discharge cycleof the cell. In some cases, the anode comprises no more than four,three, or two times the amount of lithium which can be ionized duringone full discharge cycle of the cell.

In some embodiments, when an additive is added into the electrolyte thatis added to the electrochemical cell during fabrication, the additivemay first be introduced into the cell as a part of other cell componentsfrom where it can enter the electrolyte. The additive may beincorporated into liquid, gel or solid polymer electrolytes. In someembodiments, the additive may be incorporated in the cathode formulationor into the separator in the fabrication process, as long as it isincluded in a manner such that it will enter the electrolyte insufficient concentrations. Thus, during discharge and charging of thecell, the additive incorporated in the cathode formulation or theseparator may dissolve, at least partially, in the electrolyte.

In some embodiments, a nitrogen-containing compound, as described above,can be used as an additive. When included in electrolyte 106,concentrations of the nitrogen-containing additive in the electrolytesmay be from about 0.01 m to about 2.0 m (e.g., from about 0.1 m to about1.5 m, or from about 0.2 m to about 1.0 m). Concentrations of the ionicnitrogen-containing additive when used in embodiments that do notinclude added lithium salts may vary from about 0.2 m to about 2.0 m.

In some embodiments, electrochemical cells described herein are adaptedand arranged such that electrolyte compositions are separated todifferent portions of the cell. Such separation can result in isolationof a particular species from a portion of the electrochemical cell, orat least reduction in level of exposure of that portion to the species,for a variety of purposes, including prevention of deposition of certainsolids on or within electrodes of devices of this type.

Separation of electrolyte compositions described herein can be carriedout in a variety of manners. In one set of techniques, a polymer (whichcan be a gel) is positioned at a location in the device where it isdesirable for a particular electrolyte solvent, which has relativelyhigh affinity for the polymer, to reside. In another set of techniques,two different polymers are positioned in the device at particularlocations where two different electrolyte solvents, each having arelatively greater affinity for one of the polymers, are desirablypositioned. Similar arrangements can be constructed using more than twopolymers. Relatively immiscible electrolyte solvents can be used, andpositioned relative to each other, and to other components of thedevice, so as to control exposure of at least one component of thedevice to a particular species, by exploiting the fact that the speciesmay be more highly soluble in one solvent than the other. Techniquesdescribed generally above, or other techniques, or any combination, canbe used toward this general separation methodology.

As described herein, an electrochemical cell may include an anode havinglithium (e.g., lithium metal, a lithium intercalation compound, or alithium alloy) as the active anode species and a lithiated metal oxidecathode. In these embodiments, suitable electrolytes for the lithiumbatteries can comprise a heterogeneous electrolyte including a firstelectrolyte solvent (e.g., dioxolane (DOL)) that partitions towards theanode and is favorable towards the anode (referred to herein as an“anode-side electrolyte solvent”) and a second electrolyte solvent(e.g., 1,2 dimethoxyethane (DME)) that partitions towards the cathodeand is favorable towards the cathode (and referred to herein as an“cathode-side electrolyte solvent”). In some embodiments, the anode-sideelectrolyte solvent has a relatively lower reactivity towards lithiummetal than the cathode-side electrolyte solvent. The cathode-sideelectrolyte solvent may be more reactive towards lithium metal. Byseparating the electrolyte solvents during operation of theelectrochemical cell such that the anode-side electrolyte solvent ispresent disproportionately at the anode and the cathode-side electrolytesolvent is present disproportionately at the cathode, theelectrochemical cell can benefit from desirable characteristics of bothelectrolyte solvents. Specifically, anode consumption can be decreased,and as a result, the electrochemical cell may have a longer cycle life.Furthermore, the batteries described herein may have a high specificenergy (e.g., greater than 350 Wh/kg), improved safety, and/or may beoperable at a wide range of temperatures (e.g., from −70° C. to +75°C.). Disproportionate presence of one species or solvent, versusanother, at a particular location in a cell means that the first speciesor solvent is present, at that location (e.g., at a surface of a cellelectrode) in at least a 2:1 molar or weight ratio, or even a 5:1, 10:1,50:1, or 100:1 or greater ratio.

As used herein, a “heterogeneous electrolyte” is an electrolyteincluding at least two different liquid solvents (oftentimes referred toherein as first and second electrolyte solvents, or anode-side andcathode-side electrolyte solvents). The two different liquid solventsmay be miscible or immiscible with one another, although in many aspectsof the invention, electrolyte systems include one or more solvents thatare immiscible (or can be made immiscible within the cell) to the extentthat they will largely separate and at least one can be isolated from atleast one component of the cell. A heterogeneous electrolyte may be inthe form of a liquid, a gel, or a combination thereof.

As certain embodiments described herein involve a heterogeneouselectrolyte having at least two electrolyte solvents that can partitionduring operation of the electrochemical cell, one goal may be to preventor decrease the likelihood of spontaneous solvent mixing, i.e.,generation of an emulsion of two immiscible liquids. As described inmore detail below, this may be achieved in some embodiments by“immobilizing” at least one electrolyte solvent at an electrode (e.g.,an anode) by forming, for example, a polymer gel electrolyte,glassy-state polymer, or a higher viscosity liquid that residesdisproportionately at that electrode.

In some embodiments, an anode includes a polymer layer adjacent amultilayered structure of the anode (e.g., positioned as an outerlayer). The polymer layer can, in some instances, be in the form of apolymer gel or a glassy-state polymer. The polymer layer may have anaffinity to one electrolyte solvent of a heterogeneous electrolyte suchthat during operation of the electrochemical cell, a first electrolytesolvent resides disproportionately at the anode, while a secondelectrolyte solvent is substantially excluded from the polymer layer andis present disproportionately at the cathode. For example, a firstelectrolyte solvent may reside predominately at a polymer layer adjacentthe anode. Because the first electrolyte solvent is present closer tothe anode, it is generally chosen to have one or more characteristicssuch as low reactivity to lithium (e.g., enable high lithiumcycle-ability), reasonable lithium ion conductivity. The secondelectrolyte solvent may be present disproportionately at the cathodeand, for example, may reside substantially in a separator, a polymerlayer adjacent the cathode, and/or in a base electrode material layer ofthe cathode (e.g., cathode active material layer). For example, a secondelectrolyte solvent may reside predominately at a polymer layer adjacentthe cathode, predominately in the base electrode material layer, or incombinations thereof. In some instances, the second electrolyte solventis essentially free of contact with the anode. The second electrolytesolvent may have characteristics that favor better cathode performancesuch as high lithium ion conductivity, and may have a wide liquid statetemperature range. In some cases, the second electrolyte solvent has ahigher reactivity to lithium than the first electrolyte solvent. It maybe desirable, therefore, to cause the second electrolyte solvent to bepresent at the cathode (i.e., away from the anode) during operation ofthe electrochemical cell, thereby effectively reducing itsconcentration, and reactivity, at the anode.

As described above, the first electrolyte solvent of a heterogeneouselectrolyte may be present disproportionately at the anode by residingin a polymer layer positioned adjacent a multi-layered structure.Accordingly, the material composition of the polymer layer may be chosensuch that the polymer has a relatively higher affinity to (highsolubility in) the first electrolyte solvent compared to the secondelectrolyte solvent. For instance, in some embodiments, the polymerlayer is prepared in the form of a gel by mixing a monomer, a firstelectrolyte solvent, and, optionally, other components (e.g., acrosslinking agent, lithium salts, etc.) and disposing this mixture onthe anode. The monomer can be polymerized by various methods (e.g.,using a radical initiator, ultra violet radiation, an electron beam, orcatalyst (e.g., an acid, base, or transition metal catalyst)) to form agel electrolyte. Polymerization may take place either before or afterdisposing the mixture on the anode. After assembling the othercomponents of the cell, the cell can be filled with the secondelectrolyte solvent. The second electrolyte solvent may be excluded fromthe polymer layer (e.g., due to the high affinity of the polymer withthe first electrolyte solvent already present in the polymer layerand/or due to immiscibility between the first and second electrolytesolvents). In some instances, the second electrolyte solvent may fillthe spaces (e.g., pores) within the separator and/or the cathode. Insome embodiments, the cathode can be dried prior to assembly of theelectrochemical cell to facilitate this process. Additionally and/oralternatively, the cathode (e.g., base electrode material layer of thecathode) may include a polymer that has a high affinity for the secondelectrolyte solvent. The polymer in the base electrode material layermay be in the form of particles. In some cases, the second electrolytecan reside at least partially in a polymer layer positioned adjacent thecathode.

In another embodiment, a polymer layer is formed at the anode and isdried prior to assembly of the cell. The cell can then be filled with aheterogeneous electrolyte including the first and second electrolytesolvents. If the polymer layer is chosen such that it has a higheraffinity towards the first electrolyte solvent (and/or the separatorand/or cathode may have a higher affinity towards the second electrolytesolvent), at least portions of the first and second electrolyte solventscan partition once they are introduced into the cell. In yet anotherembodiment, partitioning of the first and second electrolyte solventscan take place after commencement of first discharge of the cell. Forexample, as heat is produced while operating the battery, the affinitybetween the polymer layer and the first electrolyte solvent can increase(and/or the affinity between the separator and/or cathode and the secondelectrolyte solvent can increase). Thus, a greater degree ofpartitioning of the electrolyte solvents can occur during operation ofthe cell. Additionally, at lower temperatures, the effect may beirreversible such that the first electrolyte solvent is trapped withinthe polymer layer, and the second electrolyte solvent is trapped withinthe pores of the separator and/or cathode.

In some cases, the components of the electrochemical cell (e.g., thepolymer layer) may be pretreated (e.g., with heat) prior to use toaffect the desired degree of polymer/electrolyte solvent interaction.Other methods of partitioning the electrolyte solvents are alsopossible.

In another embodiment, the polymer layer is deposited at the anode andthe anode (including the polymer layer) is exposed to a firstelectrolyte solvent. This exposure can cause the first electrolytesolvent to be absorbed in the polymer. The cell can be formed bypositioning a cathode adjacent the anode such that the polymer layer ispositioned between the anode and cathode. The cathode can then beexposed to a second electrolyte solvent, e.g., such that at least aportion of the second electrolyte solvent is absorbed in the cathode. Inother embodiments, the cathode can be exposed to the second electrolytesolvent prior to assembly of the anode and cathode. Optionally, thecathode may include a polymer layer that preferentially absorbs thesecond electrolyte solvent more than the first electrolyte solvent. Insome embodiments, e.g., by choosing appropriate polymer(s) and/ormaterials used to form the anode and/or cathode, at least portions ofthe first and second electrolyte solvents can be separated within thecell. For instance, a higher proportion of the first electrolyte solventmay reside at the anode and a higher proportion of the secondelectrolyte solvent may reside at the cathode.

In yet another embodiment, an electrochemical cell does not include apolymer layer specifically used for partitioning at the anode or thecathode. A separator may include a different composition near the anodeside compared to the cathode side of the separator, the anode sidehaving a higher affinity for the first solvent and the cathode sidehaving a higher affinity for the second solvent. Additionally and/oralternatively, the second electrolyte solvent may be presentdisproportionately at the cathode by, for example, fabricating thecathode such that it contains a component that has a high affinity forthe second electrolyte solvent.

In some of the embodiments described herein, an electrochemical cell maybe filled with a heterogeneous electrolyte including first and secondelectrolyte solvents and partitioning of the electrolyte solvents canoccur after commencement of first discharge of the cell. Thus, in someembodiments, the first and second electrolyte solvents may be misciblebefore, but immiscible after, commencement of first discharge of thebattery. In other embodiments, the first and second electrolyte solventsare miscible before commencement of first discharge of the cell, but theelectrolyte solvents become immiscible due to heating of the electrolytesolvents during operation of the cell. In yet other embodiments, thefirst and second electrolyte solvents are immiscible before and aftercommencement of first discharge of the cell. For instance, the first andsecond electrolyte solvents may be inherently immiscible at roomtemperature, as well as during operation of the battery. Advantageously,in some embodiments, two immiscible liquid electrolyte solvents, onepresent disproportionately and the anode and the other presentdisproportionately and the cathode, do not cause additional mechanicalstress to the battery as a solid membrane may, during electrode volumechanges that occur during cell cycling.

As described herein, in some embodiments a polymer that has an affinityfor an electrolyte solvent can be dispersed within the cathode (e.g., ina base electrode material layer). For instance, the cathode activematerial layer may include a polymeric material in powder formincorporated therein. In some cases, the polymeric material is aninsoluble component in the cathode layer. For example, the polymericmaterial may be insoluble in the solvent used to dissolve the cathodeactive material. The polymer can be obtained, or modified, to have asuitable particle size and dispersed throughout the cathode byincorporation in the cathode slurry. One advantage of incorporating aninsoluble polymer with the cathode active material layer is that thepolymer can remain as discrete particles that do not coat, adsorb,and/or block the active carbon sites. In other cases, however, thepolymeric material can be dissolved, or partially dissolved, as thecathode binder in the cathode layer.

In certain embodiments including one or more polymers dispersed within alayer (e.g., insoluble polymeric particles dispersed in a cathode), thepolymers can have any suitable particle size. The average diameter ofthe polymer particles may be, for example, less than or equal to 100microns, less than or equal to 70 microns, less than or equal to 50microns, less than or equal to 30 microns, less than or equal to 15microns, less than or equal to 10 microns, or less than or equal to 5microns. Of course, a range of polymer particle sizes may be used. Forexample, in one embodiment, the polymer particles may have a size ofd10=5, d50=12, and d97=55 microns, meaning 10% of the particles werebelow 5 microns, 50% of the particles below 12 microns, and only 3% ofthe particles measured above 55 microns.

Suitable polymer materials for partitioning electrolyte solvents mayinclude the polymers described herein, such as those mentioned aboveregarding suitable polymeric materials for polymer layers (e.g., as partof a multi-layer protective structure). In some embodiments, a singlepolymer layer is in contact with an anode or cathode of anelectrochemical cell; however, in other embodiments, more than onepolymer layer can be associated with an anode or cathode. For instance,a polymer layer in contact with an anode (or cathode) may be formed ofmore than one polymer layer coated in sequence. The sequence of polymersmay include, for example, a first polymer and a second polymer, thefirst and second polymers being the same or different. Additionalpolymers, e.g., fourth, fifth, or sixth polymer layers, can also beused. Each of the polymer layers may optionally include one or morefillers or other components (e.g., crosslinking agents, lithium salts,etc.).

The thickness of a polymer layer may vary, e.g., over a range from about0.1 microns to about 100 microns. The thickness of the polymer layer maydepend on, for example, whether it is positioned adjacent the anode orcathode, whether a separator is also present in the battery, and/or thenumber of polymer layers in the cell. For instance, the thickness of thepolymer layer may be between 0.1-1 microns thick, between 1-5 micronsthick, between 5-10 microns thick, between 10-30 microns thick, orbetween 30-50 microns thick, between 50-70 microns thick, or between50-100 microns thick. In some embodiments, the thickness of a polymerlayer may be no greater than, e.g., 50 microns thick, no greater than 25microns thick, no greater than 10 microns thick, no greater than 5microns thick, no greater than 2.5 microns thick, no greater than 1micron thick, no greater than 0.5 microns thick, or no greater than 0.1microns thick.

As set forth above, in accordance with further exemplary embodiments ofthe invention, electrolyte 106 includes a nitrogen-containing groupattached to an insoluble cation, monomer, oligomer, or polymer to forman insoluble nitrogen-containing material in the electrolyte. Compounds,such as salts of K, Mg, Ca, Sr, Al, aromatic hydrocarbons, or ethers asbutyl ether may additionally or alternatively be added to theelectrolyte to reduce the solubility of nitrogen-containing compounds,such as inorganic nitrate, organic nitrates, inorganic nitrites, organicnitrites, organic nitro compounds, and the like, such that any of thenitrogen-containing compounds described herein become substantiallyinsoluble nitrogen-containing compounds as defined herein.

In accordance with various exemplary embodiments of the invention,electrolyte 106 includes about 30% to about 90%, or about 50% to about85%, or about 60% to about 80% solvents, about 0.1% to about 10%, orabout 0.5% to about 7.5%, or about 1% to about 5% nitrogen-containingadditive, and about 1% to about 20%, or about 1% to about 10%, or about1% to about 5%, or up to 4% substantially insoluble nitrogen-containingmaterial, and up to about 20%, or about 4% to about 20%, or about 6% toabout 16%, or about 8% to about 12% salt (e.g., LiTFSI).

Referring again to FIG. 1, in accordance with various embodiments of theinvention, electrochemical cell 100 includes separator 108 interposedbetween cathode 102 and anode 104. The separator may be a solidnon-conductive or insulative material which separates or insulates theanode and the cathode from each other preventing short circuiting. Thepores of the separator may be partially or substantially filled withelectrolyte.

Separators may be supplied as porous free standing films which areinterleaved with the anodes and the cathodes during the fabrication ofcells. Alternatively, the porous separator layer may be applied directlyto the surface of one of the electrodes.

A variety of separator materials are known in the art. Examples ofsuitable solid porous separator materials include, but are not limitedto, polyolefins, such as, for example, polyethylenes and polypropylenes,glass fiber filter papers, and ceramic materials. Further examples ofseparators and separator materials suitable for use in this inventionare those comprising a microporous xerogel layer, for example, amicroporous pseudo-boehmite layer, which may be provided either as afree-standing film or by a direct coating application on one of theelectrodes. Solid electrolytes and gel electrolytes may also function asa separator in addition to their electrolyte function and which permitsthe transport of ions between the anode and the cathode.

In accordance with various embodiments of the invention, separator 108may include one or more nitrogen-containing materials, such as one ormore monomers, oligomers and/or polymers selected from the groupconsisting of: polyethylene imine, polyphosphazene, polyvinylpyrolidone,polyacrylamide, polyaniline, polyelectrolytes (e.g., having a nitroaliphatic portion as a functional group), and amine groups, such aspolyacrylamide, polyallylaminde and polydiallyldimethylammoniumchloride, polyimides, polybenzimidazole, polyamides, and the like.

The composition of the nitrogen-containing material in separator 108 maybe up to 100% or about 30% to about 60%. The separator may be up toabout 20%, or about 4% to about 6% of the electrochemical cell weight.

An electrochemical cell may include any suitable current collector 112,114. A current collector is useful in efficiently collecting theelectrical current generated throughout an electrode and in providing anefficient surface for attachment of the electrical contacts leading tothe external circuit. A wide range of current collectors are known inthe art. Suitable current collectors may include, for example, metalfoils (e.g., aluminum foil), polymer films, metallized polymer films(e.g., aluminized plastic films, such as aluminized polyester film),electrically conductive polymer films, polymer films having anelectrically conductive coating, electrically conductive polymer filmshaving an electrically conductive metal coating, and polymer filmshaving conductive particles dispersed therein.

In some embodiments, the current collector includes one or moreconductive metals such as aluminum, copper, chromium, stainless steeland nickel or an alloy or alloys of such metals. Other currentcollectors may include, for example, expanded metals, metal mesh, metalgrids, expanded metal grids, metal wool, woven carbon fabric, wovencarbon mesh, non-woven carbon mesh, or carbon felt. Furthermore, acurrent collector may be electrochemically inactive or may comprise anelectroactive material. For example, a current collector may include amaterial that is used as an electroactive material layer (e.g., as ananode or a cathode such as those described herein).

A current collector may be positioned on a surface by any suitablemethod such as lamination, sputtering, or vapor deposition. In somecases, a current collector is provided as a commercially available sheetthat is laminated with one or more electrochemical cell components. Inother cases, a current collector is formed during fabrication of theelectrode by depositing a conductive material on a suitable surface.Side or edge current collectors may also be incorporated intoelectrochemical cells described herein.

A current collector may have any suitable thickness. For instance, thethickness of a current collector may be, for example, between 0.1 and0.5 microns thick, between 0.1 and 0.3 microns thick, between 0.1 and 2microns thick, between 1-5 microns thick, between 5-10 microns thick,between 5-20 microns thick, or between 10-50 microns thick. In certainembodiments, the thickness of a current collector is, e.g., about 20microns or less, about 12 microns or less, about 10 microns or less,about 7 microns or less, about 5 microns or less, about 3 microns orless, about 1 micron or less, about 0.5 micron or less, or about 0.3micron or less. In some embodiments, the use of a release layer duringfabrication of an electrode can allow the formation or use of a verythin current collector, which can reduce the overall weight of the cell,thereby increasing the cell's energy density.

As previously stated, electrochemical cells in accordance with variousembodiments of the invention may include one or more nitrogen-containingcompounds in one or more components of a cell. For example, the cell mayinclude a cathode, an anode, a separator between the anode and cathode,a non-aqueous electrolyte, and a nitrogen-containing material in one ormore of the group consisting of the anode, the cathode, and theseparator. Alternatively, the cell may include a cathode, an anode,optionally a separator between the anode and cathode, a non-aqueouselectrolyte, and a nitrogen-containing material in one or more of thegroup consisting of the anode, the cathode, the separator, and theelectrolyte, wherein, the nitrogen-containing compound is soluble orsubstantially insoluble in the electrolyte. The nitrogen-containingmaterials may be soluble, substantially insoluble in the electrolyte,attached to a moiety that is substantially insoluble in the electrolyte,and/or form part of the cathode, anode, separator, or portion(s)thereof, such that the cell portion includes a functional groupincluding nitrogen, which may be substantially insoluble in theelectrolyte. The exemplary cells may additionally includenitrogen-containing additives in the electrolyte. By way of examples,the anode; the cathode; the separator; the electrolyte; the anode andcathode; the separator and one or both of the anode and cathode; theelectrolyte and one or both of the anode and cathode; the anode, thecathode and the separator; the anode, the cathode and the electrolyte,the anode, the cathode, the electrolyte, and the separator may includethe nitrogen-containing materials as described herein.

Electrochemical cells in accordance with exemplary embodiments mayinclude a multi-layer structure interposed between the anode andcathode. Exemplary multi-layer structures are described herein as wellas in U.S. Pat. No. 8,197,971, entitled Lithium Anodes forElectrochemical Cells, issued Jun. 12, 2012 and U.S. Pat. No. 7,771,870,entitled Electrode Protection in Both Aqueous and Non-AqueousElectrochemical Cells, Including Rechargeable Lithium Batteries, issuedAug. 10, 2010, the contents of which are hereby incorporated herein byreference to the extent the contents do not conflict with the presentdisclosure.

Batteries, in accordance with various exemplary embodiments of theinvention, include one or more cells as described herein, currentcollectors (e.g., collectors 112, 114), leads or terminals (e.g., apositive lead and a negative lead) electrically coupled to thecollectors, and a casing or housing, which encapsulates at least aportion of the cell.

EXAMPLES

The following non-limiting examples illustrate a comparativeelectrochemical cell and electrochemical cells in accordance withexemplary embodiments of the invention. These examples are merelyillustrative, and it is not intended that the invention be limited tothe examples.

In the following examples and the comparative example, lithium-ionelectrochemical cells were prepared by the following steps: the anodewas vacuum deposited Li (thickness: 25 μm) on a polyethyleneterephthalate (PET) substrate with 200 nm Cu as current collector. Theporous separator used was 25 μm polyolefin (Celgard 2325), and thecathode used was LiCoO₂ coated on the aluminum substrate with capacityof 2.7-2.8 mAh/cm2, unless otherwise indicated. The above componentswere assembled in a layered structure ofanode/separator/cathode/separator/anode. The total active cathodesurface area was 33.147 cm². After sealing the cell components in a foilpouch, 0.35 mL of the respective electrolyte was added. The cell packagewas then vacuum sealed. The cells were allowed to soak in theelectrolyte for 24 hours unrestrained and then 10 kg/cm² pressure wasapplied. All the cells were cycled under such pressure. Charge anddischarge cycling was performed at standard C/8 (11.4 mA) and C/5 rate(18.2 mA), respectively, with charge cutoff voltage of 4.2 V followed bytaper at 4.2 V to 1.14 mA, and discharge cutoff at 3.2 V.

The anode morphology was studied at end of the 5th discharge by SEM. Inorder to make direct comparison of Li stripping and deposition amongdifferent cells, the amount of Li involved in the electrochemicalreaction were fixed. In other words, the charging capacity wascontrolled at 65 mAh. The charge and discharge rates were at 7.8 mA and13.7 mA, respectively, with same cut-off voltage as stated above.

Comparative Example 1

The electrolyte was a 1M lithium hexafluorophosphate (LiPF6) in a 1:1weight ratio mixture of dimethyl carbonate (DMC) and ethylene carbonate(EC) purchased from Novolyte Technologies. This electrolyte is designateas Li-ion2. As shown in FIG. 4, the discharge capacity for thiselectrochemical cell gradually decreased with each cycle. The loss ofdischarge capacity was approximately 10% by cycle 40. The recharge ratioas shown in FIG. 5 was at approximately 0.97 by cycle 40. FIGS. 6A and6B show the SEM images of anode morphology at the 5th discharge,illustrating the Li utilization in the Li-ion electrolyte was veryuneven. Moreover, the Li was porous and loosely packed with very highsurface area in comparison to the electrochemical cells containingnitrogen-containing (e.g., N—O) compound additives.

Example 1

The electrochemical cell was the same as comparative Example 1, exceptthat LiNO₃ at a concentration of about 1% (saturation) was incorporatedin the electrolyte.

Example 2

The electrochemical cell was the same as comparative Example 1, exceptthat LiNO₃ at a concentration of about 1% and pyridine nitrate at aconcentration of about 0.4% were incorporated in the electrolyte.

For both Examples 1 and 2, the fade rate of discharge capacity (FIG. 4)and the recharge ratio (FIG. 5) in the electrolyte with additives weresignificantly improved. The presence of these additives alsosurprisingly and unexpectedly improved the Li anode surface morphology.More homogeneous utilization of Li was observed (FIG. 6), and the Li wastightly packed with significantly reduced surface area in comparison tothe anode in Li-ion electrolytes. The cell cycle life increased from ˜50cycles in the standard Li-ion electrolytes to ˜90 cycles in electrolytewith LiNO3 as an additive.

Example 3

The electrolyte was the same as Example 1, except that LiNO₃ wasincorporated in the electrolyte as a suspension. Cycle life was not onlymore than doubled as that in the standard Li-ion electrolyte(Comparative Example), but also better than that in the electrolyte withLiNO₃ solution. It is believed that more LiNO₃ continuously goes intothe electrolyte solution, compensating the loss due to LiNO₃decomposition during life cycling.

Example 4

The electrolyte was the same as Example 1. The cathode used was NCM424(LiNi_(0.4)Co_(0.2)Mn_(0.4)O₂). Testing conditions were same asdescribed above for cell including LiCoO2 cathode material. Charge anddischarge currents were adjusted according to the cathode capacity, sothat the charge and discharge cycling was performed at standard C/8 andC/5 rate respectively. Both fade rate of discharge capacity, asillustrated in FIG. 7, and the recharge ratio, as illustrated in FIG. 8,for cells including an electrolyte with LiNO₃ additives weresignificantly improved.

Example 5

The electrolytes were the same as Example 3. The cathode used was NCM111(LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂). Charge and discharge currents wereadjusted according to the cathode capacity, so that the charge anddischarge cycling was performed at standard C/8 and C/5 raterespectively. As shown in FIG. 9, the cell cycle life increased from ˜80cycles in the standard Li-ion electrolytes to ˜120 cycles in electrolytewith LiNO₃ as an additive, and to ˜140 cycles in electrolyte with LiNO₃as suspension.

The present invention has been described above with reference to anumber of exemplary embodiments and examples. It should be appreciatedthat the particular embodiments shown and described herein areillustrative of the exemplary embodiments of the invention, and are notintended to limit the scope of the invention. It will be recognized thatchanges and modifications may be made to the embodiments describedherein without departing from the scope of the present invention. Theseand other changes or modifications are intended to be included withinthe scope of the present invention.

The invention claimed is:
 1. A lithium-ion electrochemical cell,comprising: a metal oxide cathode; an anode comprising lithium; aseparator between the anode and cathode; a non-aqueous electrolytecomprising one or more non-aqueous solvents and one or more lithiumsalts; and a nitrogen-containing material.
 2. The electrochemical cellof claim 1, wherein the cathode comprises a material selected from thegroup consisting of LiCoO₂, LiCo_(x)Ni_((1-x))O₂, where x is betweenapproximately 0.05 and 0.8, LiCo_(x)Ni_(y)Mn_((1-x-y)), LiMn₂O₄, andcombinations thereof.
 3. The electrochemical cell of claim 1, whereinthe nitrogen-containing compound is selected from the group consistingof inorganic nitrates, organic nitrates, inorganic nitrites, organicnitrites, nitro compounds, other N—O compounds, and amine compounds. 4.The electrochemical cell of claim 1, wherein the nitrogen-containingmaterial is soluble in the electrolyte.
 5. The electrochemical cell ofclaim 1, wherein the nitrogen-containing material is substantiallyinsoluble in the electrolyte.
 6. The electrochemical cell of claim 1,wherein the nitrogen-containing material comprises a polyelectrolyte. 7.The electrochemical cell of claim 1, wherein the cathode includes thenitrogen-containing material.
 8. The electrochemical cell of claim 1,wherein the anode includes the nitrogen-containing material.
 9. Theelectrochemical cell of claim 1, wherein the separator includes thenitrogen-containing material.
 10. The electrochemical cell of claim 1,wherein the nitrogen-containing material forms an ion-conductive surfacelayer on the anode.
 11. The electrochemical cell of claim 1, wherein theanode comprises one or more materials selected from the group consistingof lithium metal, lithium foil, lithium deposited onto a substrate, andlithium alloys.
 12. The electrochemical cell of claim 1, wherein thenitrogen-containing material comprises a functional group selected fromthe group consisting of N—O and amine, the functional group attached toa carbon chain comprising about 8 to about 25 carbon atoms.
 13. Theelectrochemical cell of claim 1, wherein the nitrogen-containingmaterial initially forms part of one or more of the anode, the cathode,and the separator.
 14. The electrochemical cell of claim 1, wherein thenitrogen-containing material comprises a nitrogen group attached to aninsoluble material selected from the group consisting of a cation, amonomer, an oligomer, and a polymer.
 15. The electrochemical cell ofclaim 1, wherein the electrolyte further comprises an N—O additive. 16.The electrochemical cell of claim 15, wherein the electrolyte comprisesabout 30% to about 90% one or more non-aqueous solvents, about 0.1% toabout 10% N—O additive, up to 4% nitrogen-containing material, and up toabout 20% LiTFSI.
 17. The electrochemical cell of claim 15, wherein theelectrolyte comprises about 50% to about 85% one or more non-aqueoussolvents, about 0.5% to about 7.5% N—O additive, up to 4%nitrogen-containing material, and about 4% to about 20% LiTFSI.
 18. Anelectrochemical cell, comprising: a cathode comprising and electroactivemetal oxide; an anode comprising lithium; a nitrogen-containingcompound; and a non-aqueous electrolyte comprising one or morenon-aqueous solvents, at least a portion of the nitrogen-containingcompound; and one or more lithium salts.
 19. The electrochemical cell ofclaim 1, wherein the cell life is greater than 90 cycles.
 20. Theelectrochemical cell of claim 1, wherein the discharge capacity ratio isgreater than 0.8 after 60 cycles.
 21. A battery comprising: a housing; apositive lead; a negative lead; and one or more electrochemical cells asdefined in claim 1.